Democrats accused former vice president Dick Cheney of abusing his power for allegedly ordering the CIA to withhold information from Congress about a secret counterterrorism program.
News of the secret program came as lawmakers from both President Barack Obama's Democratic Party and opposition Republicans engage in a bitter dispute over whether the Central Intelligence Agency adequately informed Congress, as required by law, about sensitive programs during George W. Bush's presidency.
Lawmakers vowed to hold hearings on the nature of the mysterious program, as well as efforts to keep members of the US legislature in the dark.
CIA director Leon Panetta told members of Congress that Cheney ordered the agency not to share details of the program with legislators, said Senate Intelligence Committee head Dianne Feinstein.
"I think if the intelligence committees had been briefed, they could have watched the program, they could have asked for reports on the program, they could have made judgments about the program as it went along," Feinstein said on "Fox News Sunday."
"That was not the case, because we were kept in the dark. That is something that should never happen again," she said, describing the move as "outside the law."
Democratic Senator Kent Conrad, appearing on CNN, described the alleged failure to notify Congress about the program was "a serious breach" of the law.
Representative Anna Eshoo, a Democratic member of the House Intelligence Committee, said she would call for the panel to hire an outside counsel to investigate the issue.
"We have to know who gave the order for this, who gave the order to conceal this, where did they draw the money for this," Eshoo told the Washington Post.
Eshoo said the House committee may have to issue subpoenas to interview some officials who oversaw intelligence issues during the Bush administration.
Patrick Leahy, chairman of the Senate's powerful judiciary committee, also said he would favor an investigation.
"I think it's impossible to just leave it lay when you have something like this," Leahy told CBS television.
"You can't have somebody say, well, if you're vice president, you don't have to obey the law," he said.
An unnamed intelligence official told The Washington Post that the highly secretive program was in the planning stages and never crossed the agency's threshold for reporting to congressional overseers.
Two former agency officials told the newspaper that it involved proposals to provide US intelligence agencies with a "needed capability" -- without explaining what that meant.
The latest proposal was aired in the spring of 2008 but was not carried out, the officials said, although they told The Post that it did not involve interrogations of detainees or surveillance of US-based communications, two highly controversial practices condemned by civil libertarians.
The New York Times -- which first broke the story about Cheney's alleged role -- reported that Panetta ended the program when he first learned of it on June 23.
Panetta reportedly revealed Cheney's role one day later in a closed-door briefing to members of the Senate and House intelligence committees.
"Because this program never went fully operational and hadn't been briefed as Panetta thought it should have been, his decision to kill it was neither difficult nor controversial," an intelligence official told The Times, speaking on condition of anonymity.
In May, Democratic House Speaker Nancy Pelosi charged that the US spy agency misled lawmakers in 2002 about interrogation techniques widely seen as torture, including "waterboarding," a simulated drowning method.
"If somebody told the CIA not to inform the appropriate members of Congress on information, that's wrong," said Republican Senator Judd Gregg, speaking on CNN.
Nevertheless "that isn't a reason to disassemble the CIA and make them a whipping child in the middle," Gregg said.
The Republic lawmaker said the controversy pointed to a "continued attack on the CIA and our intelligence gathering organizations" which he said "is undermining the morale and capacity of those organizations to gather intelligence."